Sierer



P. slr-:RER 2,899,674

ALARM SYSTEM 2 Sheets-Sheer:I 1

Aug. l1, 1959 Filed sept. 1e, 1954 5. Te K mi m m5, N L@ im 2Sheets-Suele?l 2 P. SIERER ALARM SYSTEM INVENTOR. IDA Yso/v ,51E/effe.BY WM UW Z MM Arron/Eri.

Aug. 11,1959

Filed sept. 16. 1954 United States Patent ALARM SYSTEM Payson Sierer,Woodhaven, N.Y., assignor to Safer Electronic Fire Alarm, Inc.,Edgewater, NJ., a corporation of New York Application September `16,'1954, Serial No. 456,558

7 Claims. (Cl. 340-218) This invention relates to alarm systems andparticularly to such systems that are used to indicate the presence offire or intruders to iire or police stations at points remote from theprotected premises and to transmit a signal to a ire or police stationor to a private agency to indicate abnormal or normal conditions, suchsystems transmitting the desired alarm or signal by means of radiofrequency energy which is coded to distinguish the sending station.

It is known to transmit an alarm or signal by means of radio frequencyenergy from a rst place which is being protected to a supervisory point,such as a police or iire station, which energy is modulated in somemanner to indicate the source of the alarm. The alarm or signal may beinitiated by a thermally-responsive switch, by a switch operated by theopening of a window or door or by the weight of an intruder, by akey-operated switch, etc., the switch setting a radio transmitter intooperation. The signal is received at the supervisory point where itoperates an alarm or recorder.

When there are several diiferent premises being protected, it usually isnecessary to modulate the transmitter at each different place beingprotected by a distinguishing code, such as a dot-dash code, in order toeliminate the need for a wide radio frequency band and several receiversand still permit ready identification of the sending transmitter. If areasonable range for such a transmitter as well as coding apparatus isto be provided, it is uneconomical to provide several such transmittersat a single place being protected. However, a single transmitter, in alarge building, for example, would provide insuicient protection, andthe use of several dispersed switches in the building for controlling asingle transmitter is not a satisfactory solution not only because theinstallation of lines is relatively expensive but also because a linewhich interconnects a switch at a re point and the transmitter may bedamaged and rendered inoperative before the switch operates.

In accordance with one feature of the invention, a plurality ofminiature radio transmitters are located at spaced points in an area orbuilding to be protected. These transmitters are not provided withcoding apparatus and are of relatively low power. They may be batteryoperated and transmit their energy either through space or over theexisting power lines. Operation of a transmitter is initiated by acondition-responsive switch, e .g., a switch responsive to a physicalcondition such as temperature or force, and the energy of thetransmitter is received by a receiver at a point in or near the area orbuilding. The receiver energizes a further, more powerful transmitterhaving coding apparatus associated therewith. It is the output of thismore powerful transmitter which is received at the supervisory point andused to operate an alarm or recorder. Y

In order to make the foregoing system inexpensive to install andoperate, I have invented a novel and simple radio transmitter which canoperate at low voltage and hence which can be operated with a smallbattery. Such 2,899,674 Patented Aug. 11, 1,959Ti ICC a transmitter hasa low output power, but the output power is suicient to cause thereceiver to operate at distances of at least one hundred feet.

In view of its small size and power requirements, the above-mentionedradio transmitter is useful in 'systems employing call boxes. Thus, thetransmitter may be installed in a call box along with a simple codingdevice such as a coding wheel driven by a spring motor for the purposeof transmitting a manually-initiated alarm. n

Of course, any alarm system must bereliable not only in the sense thatit will not fail over long periods of time, but also in the sense thatfalse alarms are a rare occurrence. When the alarm initiator isconnected to the supervisory point by wires, interference which wouldcause a false alarm is a minor problem. However, when the signals aretransmitted from the protected premises to the supervisory point byradio energy, interference can be a serious problem. Thus, interferingelectrical radiation, also called static, emanates from many sources andsuch radiation can cause false alarms in conventional alarm systemsemploying radio energy as the signalling medium. It has been suggestedthat such false alarms can be avoided by employing two-frequency radiotransmitters and two interconnected receivers. However, such a system isnot only expensive to install but also requires greater care and canfail to operate if the code transmission is interfered with.

In accordance with a further feature of the invention, a reliable alarmsystem is provided without the use of multiple-frequency transmissionand with only a single receiver at the supervisory point byincorporating circuits in such receiver which in the absence of carrierenergy prevents operation of the supervisory alarm. When Acarrier energyis being received, the alarm is operated and its operation cannot behindered by extraneous electrical disturbances. In addition, failure ofthe receiver, for example, due to loss of sensitivity, tube failure,etc., is immediately indicated by operation of the alarm in a mannerdifferent from the manner it isv operated when an alarm signal isreceived.

Accordingly, it is an object of my invention to provide an alarm systemwhich is versatile and reliable 'and which is simple and inexpensive toinstall and maintain.

Further objects and advantages of the invention will be apparent fromthe following detailed description setting forth the manner in which Inow prefer to practice the invention and from the accompanyingdrawings,in

which: Y

Fig. 1 is a combined circuit and block diagram of an alarm systemincorporating the features of the invention;

Fig. 2 is a combined circuit and block diagram illustrating one of thetransmitters forming part of the system shown in Fig. l in greaterdetail; Y

Figs. 3 and 4 are schematic showings of coding apparatus which may beemployed in connection with the transmitters shown in Figs. 2 and 5;

Figs. 5 and 5A are circuit diagrams of transmitters which may beemployed in the system illustrated in Fig. 1; and f Fig. 6 is a combinedcircuit and block diagramof the preferred form of the supervisoryreceiver forming part of the system illustrated in Fig. 1.

Referring to Fig. 1, the supervisory point, such as Aa. police or firestation or the quarters of a private protective agency, is provided witha receiver 10 for receiving radio frequency energy. The output of thereceiver 10 controls a relay 11 which may have one or more armatures12-15 and associated contacts for closingcircuits of various types ofalarm devices. For example, as shown, armature 12 closesV a circuit forlighting a lamp16, armature 13 closes a circuit for energizing a bell orgong 17, armature v14; closes a circuit for energizing the driv`- ingcircuits of a recorder 18, such as a conventional tape recorder, andarmature 15 closes a circuit which energizes the recording mechanism ofthe recorder 18. As shown inFig. l., the relay 11 operates allof suchdevices 16, 17 and 18..but, alternatively, it mayI be arranged to4operate only one of such devices. Accordingly, when radio freguency.venergy is received by receiver 10, relay 11 is energized causingoperation of the armature 12-15 and energization of theassociated alarmdevices..

If. it is .assumed that the energy receivedby the -receiver 10. is.interrupted in accordance with a predetermined code, then ,the lamp 16will flash in accordance with the code, the, gong 17Y will produce anaudible interrupted and the recorder 18 will indicate the reception of`energy. for successive periods of. time.

f A. transmitter. 19 is located at the premises being protected or at.thepoint from which it is desired to send a signal. The output of thetransmitter 19 is interrupted in" vaccordance with a predetermined codeby meansof acoder 20'which is connected to the transmitter 19 in aconventional manner as shown in greater detail hereinafter. Thetransmitter 19 is energized or caused to transmit. radiofrequency.energy by a relay 21 having one or morearmatures 22, 23, 24 and 25. Whenthe relay 21 is energized, it closes a circuit at its armature 22 forenergizing the transmitter 19., at its armature 23. it closes acircuit.for energizing the coder 20 and at its armature 25,;it'closes a circuitfor energizing a. local alarm such asa bell 25a. AtV armature 24 relay21 closes aV circuit for locking the relay 21 and thereby preventing itsdeenergization` until switch 26 is opened, such switch 26 normally beingopened manually. A locking circuit preferably lisprovided ,for ,theVrelay 21 so that when the relay 2,1v is'V energized by means hereinafterdescribed the trans- .mitter 19remains in operation until the switch 26is open, regardless ofvany subsequent changeV in the circuit which4e'n'ergizes relay 21,. However, if the circuit which initialas that towhich the receiver 10 is tuned. On the other hand, the receiver 28 istuned to a frequency different from the frequency of transmission of thetransmitter 19 so that the receiver 28 does not energize relay 21 due tothe transmission of energy by the transmitter 19.

A further transmitter 33 may be provided at the same premises or may belocated at a different point. The transmitter 313 operatesl on the samefrequency as the transmitter 19 and, therefore, any radio frequencyenergy transmitted by :the-transmitter 33. is. received'. .by `thereceiver 110.' Thus, a single receiver '-10 can the-employed to receive,at different times, signals from several -different transmittersvlocated at the same Vpoint or at difflyenergizesrelay 21 can be reliedupon to maintain the Arelay 21A inenergized condition, then armature 24and the associated locking circuit for relay 21 may be omitted.

By means of a switch 27 the relay 21 may be con- /nectedjtoa radiofrequency energy receiver 28 or to a condition-responsive switch 29having an electrical energy ysource 30 associated therewith. ln theposition of switch 27 shownin Fig. l, the relay 21 is energizedby theoutput ofjj receiver 28 so that when receiver 28v receives radio'frequency energy, the relayV 21 is energized.

` When the switch 27 is moved to its alternate position, l'the relay 21may be energized by the condition-responsive switch 29 in associationwith the source 30. Switch 29 may be any one of several conventionaltypes of switches depending upon the purpose. for which the sysftern isintended; Thus, if the circuit is intended to indicate the presence ofabnormal temperatures, the switch V29' may beA al temperature-responsiveswitch. Ifthe system is to be employed to indicate the presence ofintruder, then theswitch 29 can be a switch operated by the open- 'of adoor or window or 'by the weight of an intruder.. VIt the system is tobe employed for the sending of a signal which indicates that a watchmanhas reached a particu- 'lai-,watch point, then-the switch 29 may be akey or hand- 'operated switch.

Accordingly, when the switch 29 is closed in response to a particularcondition, the relay 21 is energizedY causing'the -transmitter totransmit bursts of radio frequency energy, the spacing and duration ofthe bursts beingV determined by the coder 20.

`If desired, the` relayA 21 may bev connected to both the :receiver 28and the switch 29 so as tobe operated when the receiver .28 receivesradio frequency energy or when iheswitch 29.is closed. For this purposethe contacts of the Aswitch 27 may be interconnected by jumpers3'1. and32 indicated in dotted lines in Fig. l.

` It will be understood that the vfrequency of the radio frequencytransmission of transmitter 1.9 .is the .same

ferent points. The transmitter 33 is energized and its output isinterrupted by-means of av switch and motor-driven coder 34 which may,for example, include switch 29 and coder 20 described above.

The premises being protected may be located. at arelatively longdistance, fromthe supervisory point andv hence from the receiver 1.0.Therefore, in order to provide ample power for reliable operation .andfor different types of installations, the transmitters 19 and 33 shouldbe of relatively large size and power output. In addition,. in order topermit personnelV at thesupervisory point to distinguish which ofthetransmitters 19 and V33V is transmitting, the outputs of thetransmitters '19 and 33 must be modulated with. a distinguishing code.Accordingly, it is necessary to associate withthe transmitters 19 tand33 coders as indicated at 20 and 34. 'Ihusthe transmitter employed fortransmitting energy from the protected premises tothe ,supervisory pointmust be relatively large and expensive, makingV such. transmittersunsuitable for .dispersalaround the premisesbeing protected. However,for the reasons set forthahove, a` single. transmitter with a vsingleswitchv or a. single transmitter. withV a plurality of switches doesnot. provide a satisfactory installation in certain cases, for example.in a. largeV building. lil order Vto avoid. the need for theinstallation of4 several switches. connected to. the transmitter IbyWires and in orderto avoid. the use of. several of the more expensivetransmitters, the valarm system. ofthe invention comprises the receiver28 connectedto the transmitter 19.Y as selt forth. above .and-apluralityof low power, inexpensive Vtransmitters 35 .and .3.6, which. latter.transmitters. may be llocated.,atvarious points. about. the premises tobe protected.

Each..ofl the.V transmitters 3.5 and 316 is connected to .and-controlledbya.condition-responsive switch similar to the.switch.29 previouslydescribed. Thus, ,the transmitter 35. -is connected. to and controlledby conditionresponsive switch 3 7 and the transmitter 36 is connected toand. controlled ,by` acondition-responsive switch. 38 so that when the.associatedY switch Vis operated,VV .the transmitter 3.5.-or 36continuously transmits radio frequency energy at a frequency to which,the receiver 28 Ais tuned, causing the receiver ,28. to energize therelay 21 and hencecausing the transmitter 19 to transmit coded radiofrequency energy toV the. receiver 10.

Each vofthe transmitters 35 and 36 maybe provided with an. antenna .such`as .the antennas 39` and`40 so that the.V radio frequency energy istransmitted through space to. thereceiver 28 which is similarly equippedwith an antenna-4.1. However, ifdesired, carrier current transmissionover the power linesmay be employed for transmitting `the radioYfrequency` energy from transmitters 35 and l.3.6, toV the, receiver 28.In this type of installation theftransmitters 3 5 and 3.6 .are connectedto the receiver 28 by meansofpowerlines 42`.and 434 indicated in dottedlines .in Fig. 1 andthe antennas 39--41 may be omitted.

ReferringtoFig. .2, .the .transmitter 19fof Fig. lisshown therein ingreater detail.` Thus, the transmitter. 19 may comprise a radiofrequency oscillator .44 whose output isfcoupledrto-the power amplifier45. Filament energy is supplied to-.the .oscillator 44-andztheamplifier-.45. .by a transformerV A464 whose. primary winding. 47-isjconnected to a'source of electrical power48 by means of the arma!ture 22 of relay 21. Transformer 46 has a 'high voltage winding 49 and arectifier filament winding 50, which windings are energized when theprimary winding 47 is connected to the source 48 by the relay 21. Theoutput of winding 49 is rectilied lby a conventional rectiiier tube 51so that a high D.C. voltage is present on line 52 at the output of thelilter comprising a choke 53 and a pair of capacitors 54 and 55. Theoutput of the filter is connected to the oscillator 44 by line 56 and isconnected to the power amplifier 45 by lines 57 and 58, the lines 57 and58 being connected by a contacter 59 forming part of the coder 20. Thecontactor 59 rides on the periphery of a serrated wheel 60 which isdriven by an electric motor 61, the motor 61 being connected to thepower source 48 through the armature 23 of relay 21.

Thus, when the relay 21 is energized, the transformer 46 is energizedsupplying iilament power to the oscillator 44 and the power amplifier 45and supplying high voltage energizing power to the oscillator 44. At thesame time, the motor 61 commences to operate and through a suitable gearreduction drive forming part of the motor 61 the coding wheel 60 isrotated. At the contactor 59 the high voltage for energization of poweramplifier 45 is interrupted at predetermined intervals so as to causethe radio frequency energy output of the power amplifier 45 to take theform of bursts of radio frequency energy which may have the same ordifferent durations. Thus, by the transmitting bursts of radio frequencyenergy of different durations and sequence, a large number of diiierenttransmitters may each have an identifying code. The output of the poweramplifier 45 appears across the line 62 which, as shown in Fig. l, isconnected to a suitable antenna 63.

Although in the :alarm system shown in Fig. 1 the transmitter 19 isenergized by means of a condition-responsive switch 29 or by means ofthe receiver 28, it is also possible to operate transmitter 19 so thatits transmission is initiated manually. Thus, it may be desirable toincorporate the transmitter 19 in a call box for the purpose oftransmitting an alarm manually. With such an arrangement themotor-driven coder 20* and the relay 21 shown in Figs. l and 2 arereplaced lby the switching and coding apparatus shown in Figs. 3 and 4.In one form the apparatus of Figs. 3 and 4 comprises an electric motor64 having associated therewith a reduction drive (if required) for thepurpose of reducing the speed of the coding wheel 65 to the desiredvalue. Coding wheel 65 is mounted on the output shaft 66 of the motor 64and has a plurality of teeth 67 and 68 on the periphery thereof. It willbe noted that the teeth 67 are wider than the teeth 68 and the teeth 67and 68 are arranged in spaced groups. With the arrangement shown, thetooth 67 maintains the contacter 59 in contact with its contact 69 alonger period of time than the teeth 68. Accordingly, when the roller 70of the contactor 59 is riding on a tooth 67, the transmitter 19 iscaused to transmit radio frequency energy for a period of timeindicating a dash and, when the roller 70 is riding on top of a tooth68, the transmitter 19 is caused to transmit radio frequency energy fora period of time indicating a dot. When the roller 70 is between theteeth, the transmitter 19 does not transmit radio frequency energy.

The switch arms 71 and 72 take the place, respectively, of armatures 23and 22, the arm 71, when operated, energizing the motor 64 and the arm72, when operated, energizing the transmitter 19 as described above. Theswitch arms 7 i and 72 are operated by an arm 73 which is mounted on ashaft 7 4 and turns therewith. Shaft 74 is manually rotatable by meansof a knob or lever (not shown) and, 1hence, when the shaft 74 isrotated, the transmitter 19 and the coding wheel driving motor 64 areset into operation.

To prevent the opening of the switch arms 71 and 72 after thetransmitter 19 has been set into operation, an

arm 75 is also mounted on the shaft 74 so as to be turned therewith andin the rotated position of the shaft 74 this arm 75 engages a latch 76which holds the arm 73 in a position such that the transmitter 19 andthe motor 64 are energized until the latch 76 is released. Accordingly,the operator merely rotates the shaft 74 and then releases it to causethe transmission of coded radio frequency energy by transmitter 19.

In some cases it may not be desirable to employ an electric motor fordriving the coding wheel 65. In such cases the motor 64 may be aspring-driven motor and the switch arm 71 with its associated contactmay be omitted.A However, when the motor 64 is a spring-driven motor, awheel or cam 78 driven with a coding wheel 65 is also provided and thiswheel or cam 78 has a notch 79 therein for receiving a tongue 80 on thearm 73. Accordingly, as long as the tongue 80 is within the notch 79 thecoding wheel 65 is prevented from rotating. However, when the shaft 74is rotated manually, the tongue 80 is withdrawn from the notch 79permitting the Wheel 78, and hence the coding wheel 65, to rotate. Thecoding wheel 65 continues to rotate after its initial release until thelatch 76 is released as explained above or until the spring-driven motoris unwound. The mechanism is reset merely by releasing the latch 76 andby rewinding the spring motor 64.

Fig. 5 shows a circuit diagram of one type of simple and inexpensivetransmitter which may be employed at 35 and 36 in Fig. 1. A coder 81 ofthe type shown in Figs. 3 and 4 is also shown in Fig. 5, but in theinstallation shown in Fig. l the coder 81 is omitted.

The transmitter shown in Fig. 5 comprises a vacuum tube 82 having anodeelectrodes 83 and 83a, control electrodes 84 and 84a and cathodeelectrodes 85 and 85a comprising a filament 85b. One end of the lament85b and the cathode electrodes 85 and 85a are connected to ground andthe control electrodes 84 and 84a are connected to a grid drivingwinding 84b, the center tap of which is connected to ground by aresistor 86. One end of the power source 87 which may, for example, be abattery, is connected to one end of the filament 85b and the oppositeend of the source S7 is connected to the opposite end of the lament 85bby the conditionresponsive switch 37. This opposite end of the source 87is also connected to the anode electrodes 83 and 83a through anisolating impedance in the form of a choke 88 and a tunable inductance89, the inductance 89 with the stray capacities and the circuits coupledthereto forming a resonant circuit. The inductance 89 is coupled to theantenna 9G by a coupling loop 91 and is connected at its ends to theanode electrodes 83 and 83a. The inductance 89 is also magneticallycoupled to the winding 8417 to supply energy to the control electrodes84 and 84a of the magnitude and phase necessary to produce radiofrequency oscillations.

It will be noted that the only source of energizing potential for thetube 82 shown in the Fig. 5 is the source 87 which supplies the energyfor heating the filament 85b. Thus, the circuit shown in Fig. 5 isunconventional in that the potential of the source for the anodeelectrodes 83 and 83a is the same as the potential between the ends ofthe filament 85b. I have found that a Vacuum tube such as a tubedesignated as a 12AT7 will produce oscillations at a low power levelwith the circuit arrangement shown in Fig. 5 and with the anodeelectrodes 83 and 83a connected to the source of energy for the filament85b. Of course, it will be apparent that, although I have shown theresonant or tuned circuit comprising the inductance 89 connected to theanode and control electrodes of the tube 82 in one manner, the tunedcircuit may also be coupled to one or more of these electrodes in otherconventional manners.

The transmitter shown in Fig. 5 may be made very small in size and isinexpensive to install and maintain since the source 87 is required tosupply only a relatively 7 low voltage, ie.g;, 6 volts, and there is nodrain on the source 87 `.until the switch 37 is closed.` The source `87maybe small-in size since its .output voltage `is 10W and since iti will'have to deliver energy to the tube 82 and it'sassociated circuits foronly a relatively short period of time after the switch- 37 is closed.

As--pointed `out above, the circuit shown in Fig. does not include thecoder 81 when it forms part of the circuit shownV to the left' of Fig.l. However, if desired, the circuit shown in Fig. 5 may form part of acall box ins'tallation provided only a relatively short signalling rangeisi-required such as'. inv al building. Thus, the coder 81 maybeconnected lin the circuit aslshown in Fig. l so as to interrupt -theradio frequency energy transmitted from theantenna 90 in accordance withan identifying code. The coder A81 may take the form of the modifiedembodiment described inconnection with Figs. 3 and 4 and may, forexample, include the coding wheel 65 and its associatedrco'ding parts,the coding wheel 65 being driven by a springwound motor. In such asystem the frequency of operation of 'the transmitter shown in Fig. 5will be the same-as the frequency to which the receiver is tuned so thatthesignals transmitted by the transmitter of Fig. 5 would be received bythe receiver 10 and would operate'oneor more of the alarms shown in Fig.1 in the same manner as transmitter 19 operates such alarms.

Fig. 5A shows a circuitdiagramvof a further type of simple andinexpensive' transmitter which may be em ployedat 3S and36 in Fig. l andwhich maybe employed in p'lace'of'the transmitter'shown lin Fig. 5. Asindicated in connection with Fig. 5, the-coder' S1 shown inFig. 5A wouldbeomitted when the transmitter is employed-in an installation of thetype shown'in Fig. l', but in a different type-'of-Uinstallation thecoder S1 may be employed in the manner set forth inconnection with Fig.5.

Theftransmitter shown in Fig. 5A comprises-a vacuum tube 175 having ananode electrode 176, la control electrede-177, a suppressor electrodey178, a further control o1'- screen electrode 179, and a cathodeelectrode 180 comprising a filament 181. Oneend of the filament 131 andthe cathode electrode 180 Vare connected to ground and to one end of thepower sourcev182. Control electrode-177 isconnected to Iground through aresistor 183 and is-connected to one end -of a frequency-controlling,piezo-electric crystal 184. The crystal 184 acts a's a resonant or tunedcircuit for controlling the frequency of? the oscillations of theAtransmitter shown in Fig. 5A andthe opposite end thereof is connected tothe anode electrode. 176. Thevropposite end of the source 182 isconnectedlto'the opposite endof the filament 181 by' thecondition-responsive switch 37. This opposite endfof'the source 182is'also connected to theanode-electrode 176 through. the switch 37 and thecoder Si and through a choke 185 to Which the antenna 90 is magneticallycoupled by the loop 91. The opposite end of the` source 182 isalsoconnected to the screenelectrode1f79 through the switch 37 and .atunable inductance 186 which is employed in a conventional-manner toestablish the feedbackconditions required to produce oscillations.

The transmitter shown in Fig. 5 is unconventional in that the. solesource ofenergy for the vacuum tube v1.75 is the power. source2'182whichlsupplies heating energy for the. filament 181. Thus, the D.C. potentialapplied to theanode electrode 176 is the same as -the potential-betweenthe endsof the larnent 181. I have found that .arvacuumttube of the'typedesignated as a 6Al5 will producefoscillations'at a lower. powerlevel with the circuit arrangement shown'in Fig. 5 and with the anodeelectrode. 176f-connected to the-source of energy forthe iilamentv 181-.Accordingly, the transmitter shown in Fig. 'Aihas the V.advantages ofthetransmittershownin Fig. 5 and, in addition, the transmitter shown inFig. 5A has Vagvery stable oscillation frequency since the transmitteris'crystal controlled.;

.ASrpOinted'routaboi/e, anyhalarm systemmust betreliable not only inthe'siensefthat. it-willnot failzover long. periods offtime, but alsoVin the sense `.that false alarms If the radiation :from Such `sourcesis' receivedby there.`

ceiver 10, :for example, and-the'rfeceiver 1 0 isa-conventionalreceiver, the Yradiation will cause ,operation ofthe relay 11 and hencewill cause .operation ofthe -.a1arm's` associated therewith. I n thismanner the alarms may he operated from time to time'even though itwouldrlrbe pos.- sibleto ydistinguisl'lsuch improper operationV from theproper loperation thereof by the coded ,transmission from transmitter19. However, iin addition, such Iradiation might :occur duringtheqtransmissionfof the desired radi'- ation from the transmitter 19 andmightcausethe alarmsV toindicate an erroneous code.v For these reasons.,the alarm systems of my-invention' include a-specialtypeof receiverwhich -is shown partly in block vform andi partly incircuit diagram inFig. 6.

Referring to Eig. 6, vthe radio v frequency energy `from a remotetransmitter such as the transmitter 1,9 is/ received-by antenna 9 3,amplitiedfby the ampliier 94, con verted to an intermediate frequency bythe AI 11i X er;95 and the oscillator -96 and thefresultingenergy latintermediate frequency is amplified by the amplifier 97. These por.-tions ofi the receiver are conventional in Vrnany known types o freceivers vand 4int particular in receivers in alarm systems'eoftheprior art.

Insteadeof following thefconventionalpractieeof merely detecting andamplifying the output ofY the intermediate frequency amplifier 97, thereceiver used `in the alarm system -of my invention-comprises Va pair oflimiting amplifiers 9 8 and 99, the output ofthe latter amplifier beingdetected by thedetector 100. A filter comprising. the resistor101 andthe-capacitors 102 andf 103isfeonnected between the output of,the'detector' 100 and an amplifier stage 104; The ilter attenuatesenergy at intermediate frequency and passes lower 4frequency signalssuch as noise signals.- The-noise signals are amplified by the amplifierstage 104 and rectified in the rectifier ,circuit 105. Therectitednoisesignals provideaibias for alDC. amplifier stage 106 whicheontrolsrelayli. Thus, when noise signals'are transmittedthroughiilterjltilparnplified by` amplifier '104and rectified `by'rectiter 105,afnegative bias isproduced at the amplierstage 106 whichpreventsoperation ofthe relay 11. However, whenthenoisevsig nalsare nolonger'present, the'amplifier stage 106- turns on and 4energizestherelay 11 vcausing the alarmv asso* ciated therewith to operate.Therefore, it willbe apparent that lwhen undesired electrical radiationisreceived by the receiver and in the absencevof the desired-radi'-ation, the `relay 1-1 willl not be operated' andhe'nce the alarms willalsov notbe operated. In addition, if the sensitivity of the stages ofthereceiver lpreceding the arnpliier stage '106 is reduced orifonefofvthe stagesprecedingthe stage 106 becomes inoperative, the relayl11 will become Aenergized 'and will -remainenergized .indicating by.the continuous operation of one of `the alarm-s that the receiver isfailin'gto operateproperly.

On the other hand, if undesired'radiation is received by the receiverduring reception of the desired'radiation, such interfering radiationwill not cause energization of the relay 11 or operation of the alarmsbecause the limiting amplifiers 98 and 99 will prevent such interferingradiation from producing signalsat the output of the detector 100. SuchAaction of the limiting amplifiers 98 and 99 will'be understood'rea'dilyby those skilled in the art and need not be described in detail herein.

Referring'to Fig.` 6, the output stage of'the'lF" ampliiier `97 isindicated diagrammatically at 107. Th'eoutput lstagel 107 is connected'inseries with ares'istorll 110 of the vacuum tube 111. Tube 111comprises a further control or screen electrode 112, suppressorelectrode 113, anode 114 and a cathode 115. The suppressor electrode 113and the cathode 115 are connected to ground as shown and the screenelectrode is connected to the high voltage source indicated by thesymbol B-lthrough a resistor 116 and resistor 117. Screen electrode 112is by-passed to ground =by capacitor 118. Anode 114 is connected to thehigh voltage source through a coil 119 having a high impedance at theintermediate frequency and through the resistor 117. To lower thevoltage applied to the anode 114 and -the screen electrode 112, adropping resistor 120 is connected between one end of the coil 119 andground. The output of the limiting amplifier 98 is coupled to the inputof the limiting amplifier 99 by capacitor 121 which is connected to thecontrol electrode 122 of the vacuum tube 125. Tube 125 may be the sameas tube 111 and hence-may comprise suppressor electrode 124, screenelectrode 123, anode 126 and a cathode 127. As before, suppressorelectrode 124 and cathode 127 are connected to ground as shown. Screen`electrode 123 is connected to the high voltage source through aresistor 128 and a resistor 129 and is by-passed to ground for energy ofintermediate frequency by the capacitor 130. Anode 126 is connected tothe high Voltage source through the primary winding 131 of thetransformer 132, said winding 131 being shunted by capacitor 133, anisolating resistor 134 and resistor 129. To lower the voltage applied tothe anode 126 and to the screen electrode 123, a dropping resistor 135is provided.

Transformer 132 has a second winding 136 Whose ends are connected to theanodes 137 and 138 of a pair of dode vacuum tubes 139 and 140. Thewinding 136 is shunted by a capacitor 141 and the transformer may betuned by capacitor 141 and capacitor 133 or it may be tuned in any otherwell known manner so as to pass energy at intermediate frequency. Aportion of the energy of intermediate frequency is coupled to thejunction point of a pair of resistors 142 and 143 by a capacitor 144.The cathodes 145 and 146 are connected to the opposite ends of resistors142 and 143.

When no radio frequency energy is being received from the transmitter 19shown in Fig. 1, noise signals appear across the resistors 142 and 143and are passed by the filter including the resistor 101 and thecapacitors 102 and 103 to the input of amplifier stage 104. However,whenever radio frequency energy is received by the receiver fromtransmitter 19, the limiting amplifier stages 98 and 99 are driven tosaturation even though the received energy is of a very low level. Suchoperation of the limiting amplifiers 98 and 99 squelches the noisesignals and hence during reception of radio frequency energy from thetransmitter 19 no noise signals are present across the resistors 142 and143. It is to be noted that only the reception of radio frequency energyof the proper frequency Iby the receiver will cause the noise signals todisappear.

The output of the filter is connected to amplifier stage 104 whichcomprises a Vacuum tube 147 having a cathode 148, a control electrode149, screen electrode 150, a suppressor electrode 151 and an anode 152.The suppressor electrode 151 is connected to the cathode 148 and thecathode 148 is connected to ground through a resistor 153 which controlsthe bias on the tube 147 and which controls the amplitude of the signalssupplied to rectifier 105. A resistor 154 is connected between the highvoltage source and one end of resistor 153 for providing a fixed bias onthe tube 147. The output of the filter is coupled to the controlelectrode 149 by a capacitor 155, the control electrode 149 beingconnected to ground through a resistor 159.

The screen electrode of tube 147 is connected to the high Voltage sourcethrough a resistor 156 and is bypassed to ground by a capacitor 157.Anode 152 is 10 also connected to the high voltage source through aresistor 158.

As mentioned above, the amplifier stage 104 amplifies the noise signalsappearing at the output of the filter and supplies such amplified noisesignals to the rectifier circuit 105. The rectifier circuit comprises apair of diodes 160 and 161 having anodes 162 and 163 and cathodes 164and 165. The cathode 164 of diode 160 s connected to the anode 163 ofdiode 161 and the output of amplifier 104 is coupled to the junctionpoint of the cathode and anode by the capacitor 166. The anode 162 isconnected to the control electrode 167 of tube 168 forming part of theamplifier stage 106. A resistor 169 is connected between the controlelectrode 167 and ground and is by-passed by a capacitor 170 so as toprovide a substantially fixed -bias on the control electrode 167 Whennoise signals are amplified lby the stage 104.

The diodes 160 and 161 are so poled that the voltage at the controlelectrode 167 is negative with respect to ground when noise signals areamplified by the stage 104 and the magnitude of the bias is such thatthe tube 168 is cut off or substantially cut off with the magnitude ofthe high voltage applied to the anodes 171 and 176 thereof. The cathodes173 and 174 of the tube 168 are connected to ground as shown. The anodes171 and 176 are connected to the high Voltage source through the coil ofrelay 11 and hence when the tube 168 is cut off or substantially cutoff, no current or substantially no current flows through the coil ofrelay 11. Accordingly, the relay 11 is de-energized and the armaturesthereof are in the positions shown. However, when the noise signals aresquelched by the limiting action of the amplifiers 98 and 99, there isyno bias developed across the resistor 169 and the ltube 168 becomesconducting or more conducting. When tube 168 becomes sufficientlyconducting, the current in relay 11 operates the armatures thereof andhence operates the alarm or alarms associated therewith as shown in Fig.1.

It will be apparent from the foregoing that the receiver forming part ofthe alarm system of my invention not only prevents operation of thealarms from interfering, undesired radiation, but also preventsinterference with the reception of desired radiation and operation ofthe alarms thereby in the desired manner. Also, if the receiver losesits sensitivity so that noise signals produce an insufficient voltageacross the resistor 169 or if the stages preceding the stage 106 becomeinoperative, the relay 11 will be continuously energized and hence willcause continuous operation of one of the alarms actuated by the relay11. In this way, the receiver is self-monitoring and improper operationor failure can be readily detected.

While the invention has been described with reference to the preferredforms thereof, it will be understood by those skilled in the art, afterunderstanding the invention, that modifications and changes may be madetherein without departing from the spirit and scope of the invention asdefined bythe claims appended hereto.

What is claimed as new and what I desire to secure by Letters Patent ofthe United States is:

1. An alarm system comprising a radio frequency energy transmittercomprising a source of radio frequency energy, and coding meansconnected to said source for interrupting said energy in accordance witha predetermined code; switching means for energizing said coding meansconnected thereto; a receiver spaced from said transmitter and adaptedto receive radio frequency energy from said transmitter, said receivercomprising a limiting amplifier, a detector connected to said amplifier,said arnplifier and detector providing low frequency signals at theoutput of said detector in the absence of said radio frequency energyand substantially suppressing said low frequency signals when said radiofrequency is received, a filter circuit connected to the output of saiddetector andadapted to attenuate high frequency signals and t0 passysaid low frequency signals, a further amplifier connected to said filterfor amplifying said low frequency signals, a rectifier connected to saidfurther amplifier for rectifying the amplified low frequency signals andfor thereby providing a biasing voltage upon receipt of said lowfrequency signals, and a control amplifier connected to said rectifierand controlled by said biasing voltage; and an alarm circuit connectedto said'control amplifier and' controlled thereby, said alarm circuitcomprising relay means connected to said control amplifier and energizedthereby and an alarm connected to and operated by vsaid relay means,said alarmY being disabled by said relay means during the presence ofsaid lower Vfrequency signals and beingy operated by said relay meansVin absence of said lower frequency signals.

2. An alarm system comprising a radio frequency energy transmittercomprising meansfor generating radioy frequency energy,1 neans fortransmitting said lastmentioned energy connected to said generatingmeans and coding means connected to one of said generating andtransmitting means for interrupting the transmission of saidenergy inaccordance with a predetermined code; switching means for energizingsaid coding means and said generating means connected thereto; areceiver space d from said transmitter and adapted to receive radiofrequency energy from said transmitter, Ysaid `receiver comprising alimiting amplifier, a detector connected to said amplifier, saidamplifier and detector providing audio yfrequency noise signals at theoutput of said detector yin the absence Vof said radio frequency energyand substantially suppressing said audio frequency noise signals whensaid radio frequency energy is received, a filter circuit connected tothe output of said detector and adapted to attenuate radio frequencysignals and to pass audio frequency noise signals, a further amplifierconnected' to said filter for' amplifying said noise signals, arectifier connected to said further amplifier for rectifying theamplified noise signals and for thereby providing a biasing voltage uponreceipt' of said noise signals, and a control amplifier connected'toVsaid rectier and controlled by said biasing voltage; and an alarmcircuit connected to saidl control amplifierand controlled thereby, saidalarm circuit comprisi'rig relay means connected to said controlamplifier and energized thereby in" theV absenceof-noise signals andvice versa" and an alarm connected to and operated by said relaymeans inthe energi'zed'condition thereof.

3. An alarm system comprising a first transmitter lfor transmittinguncoded radio frequency energy, said transmitter comprising means forgenerating said radio freqiiency energy and means forY initiatingoperation of said generating means connected thereto comprising acondition-responsive switch; a iirst'receiver spaced fromV saidtransmitter but adapted to receive radio frequency energy from saidtransmitter; a second radio Vfrequency energy transmitter comprisingmeans for generating radio frequency energy, means for transmitting saidlast-mentioned energy connected to said generating means and codingmeans connected to one of Vsaid generating and transmitting means forinterrupting the transmission of said last-mentioned energy inAaccordance with a predetermined code; switching means for energizingsaid coding means and said generating means connected thereto, saidswitchingmeans being connected to said first receiver and being operatedupon'receipt of radio frequency energy bysaidffirst receiver fromsaid'first transmitter; a second receiver spaced-from said secondtransmitter and adapted tol receive radio frequency energy from saidsecond transmitter,=said ksecond receiver comprising a limiting amplifier, :adetector connected to said amplifier, a filter circuit connectedto the output of said detector and adapted to attenuate radio frequencysignals and to pass noise signais, a further amplier connected to saidfilter for amplifying said noise signals, a rectifier connected to saidfurther amplier for rectifying the amplified noise signals and forthereby providing a biasing voltage upon receipt of saidl noise signals,and a control amplifier connected to said rectifier and controlled bysaid biasing voltage; and an'alarm circuit connected to said controlamplifier and' controlled thereby, said alarm circuit comprising relay`means .connectedto said control amplifier and energized thereby and analarm connected to and operatedlv by said relay means.

4'. An alarm system comprising a first transmitter for transmittinguncoded radio frequency energy, said transmitter comprising a vacuumtube having anode, control and cathode electrodes, said cathodeelectrode including a filament, a turned circuit coupled between saidanode and said control electrodes," means interconnecting said controland; saidv cathode electrodes, a source of electrical energy for heatingsaid filament connected at one end to s aidfilament and -tosaid cathodeelectrode and vmeans for 'ccnnecting the opposite end of said4 source tosaid anode electrode andV to said filament comprising a temperatureresponsive switch'connected to said opposite end and to said filamentand means interconnecting said switch and said tuned circuit, saidsource being the source of electrical energy for said anode electrode; afirstV receiver spaced from said transmitter but adaptedl to receiveradio frequency'A energy from said transmitter; a second radio frequencyenergyv transmitter comprising means vfor generating radio frequencyenergy, means for transmitting said last-mentioned energy connected tosaidf generating means and coding means connected to one of saidgenerating andtransmittin'g means for interrupting the transmission ofsaid lastjmentioned energy in accordance with a predeterminedA code;switching means for energizing said coding means and said generatingmeans connected thereto, said switching means being connected tosaidifirst receiver and being operated upon receipt of radio frequencyenergy by said first receiver from" sait first transmitter; a secondreceiver spaced from' said' sec ond transmitter andadapted to lreceiveradio frequency energy from said second transmitter, said secondreceiver comprising' a limiting' amplifier, a detector connected to saidamplifier, a` filter circuit connected to said detector and adapted toattenuate 4radio frequency signals and' to pass noise signals, a furtheramplifier connected to said filter for amplifying vsaid noise signals, arectifier connected to said further amplifier for yrectifying the ampli;fied noise signals and for thereby providing av biasing voltage uponVreceipt of said noise signals, and a con; trol amplier connected tosaid rectifier and controlled by said biasing voltage; and an alarmcircuit connected to said control amplifier and controlled thereby, saidalarm circuit comprising relay means connected to said control amplifierand energized thereby in the absence ofV noise signals and vice versaand an alarm connected to and operated by said relay means in theenergized condition thereof. t

5. An alarm system comprising a first transmitterffor transmittinguncoded radio frequency energy, said transmitter comprising Va vacuumtube having anode, control and cathode electrodes, said cathodeelectrode including a filament, a tuned circuit: coupled to said anodeand said control electrodes, a resistor interconnecting said controlyandsaid cathode'electrodes, a source of electn'i cal energy forheating` said filament connected at one end to said filament and ltolsaidcathode electrode'aud means for connecting the opposite endA of saidsource toy said anodel electrode and toV said filament comprising atemperature-responsive switch connected to said opposite end and to saidfilament and a choke connected to said switch and to said tunedcircuit,vsaid source being lthe sourceV of elcctiical energy for saidanode electrode; av first receiver spaced from said transmitter butadapted to receive radio frequency energy `from said transmitter; asecond radio frequency energy transmitter' comprising means forgenerating radio frequency energy, means .for `transmitting saidlast-mentioned energy -connected tosaid generating means and codingmeans connected to one of said generating and transmitting means forinterrupting the transmission of said last-mentioned energy inaccordance with a predetermined code; switching means for energizingsaid coding means and said generating means connected thereto, saidswitching means being connected to said first receiver and beingoperated upon receipt of radio frequency energy by said first receiverfrom said first transmitter; a second receiver spaced from said secondtransmitter and adapted to receive radio frequency energy vfrom saidsecond transmitter, said second receiver comprising a limitingamplifier, a detector connected to said amplifier, a filter circuitconnected to` said detector and adapted to attenuate radio frequencysignals and to pass audio frequency noise signals., a further amplifierconnected to said filter for amplifying said noise signals, a rectifierconnected to said further amplifier for rectifying the amplified noisesignals and for thereby providing a biasing voltage upon receipt of saidnoise signals, and a control amplifier connected to said rectifier andcontrolled by said biasing voltage; and an alarm circuit connected tosaid control amplifier and controlled thereby, said alarm circuitcomprising relay means connected to said control amplifier and energizedthereby in the absence of noise signals and vice versa and an alarmconnected to yand operated by said relay means in the energizedcondition thereof.

6. In an alarm system comprising a transmitter for transmitting radiofrequency energy which is interrupted in accordance with a predeterminedcode, a receiver spaced from said transmitter and adapted to receiveradio frequency energy from said transmitter, said receiver comprising alimiting amplifier, a detector connected to said amplifier, saidamplifier and detector providing low frequency signals at the output ofsaid detector in the absence of said radio frequency energy andsubstantially suppressing said low frequency signals when said radiofrequency is received, a filter circuit connected to the output of saiddetector and adapted to attenuate high frequency signals and to passsaid low frequency signals, and means connected to said filter circuitfor providing a biasing voltage upon receipt of said low frequencysignals; and an alarm circuit connected to said last- 14 mentioned meansand controlled by said biasing voltage, said last-mentioned circuitbeing energized by said last-mentioned means in the absence of lowfrequency signals and vice versa.

7. In an alarm system comprising a transmitter for transmitting radiofrequency energy which is interrupted in accordance with a predeterminedcode, a receiver spaced from said transmitter and adapted to receiveradio frequency energy from said transmitter, said receiver comprising alimiting amplifier, a detector connected to said amplifier, saidamplifier and detector providing loW frequency signals at the output ofsaid detector in the absence of said radio frequency energy andsubstantially suppressing said low frequency signals when said radiofrequency is received, a filter circuit connected to the output of saiddetector and adapted to attenuate high high frequency signals and topass said 10W frequency signals, a further amplifier connected to saidfilter for amplifying said low frequency signals, a rectifier connectedto said further amplifier for rectifying the amplified low frequencysignals and for thereby providing a biasing voltage upon receipt of saidlow frequency signals, and a control amplifier connected to said rectierand controlled by said biasing voltage; and an alarm circuit connectedto said control amplifier and controlled thereby, said alarm circuitcomprising alarm means connected to said control amplifier and energizedthereby in the absence of low frequency signals and vice versa.

References Cited in the le of this patent UNITED STATES PATENTS1,497,194 Norden et al June 10, 1924 1,930,525 Levy Oct. 17, 19332,116,372 Weld May 3, 1938 2,236,822 Hershey Apr. 1, 1941 2,447,438Strutt et al Aug. 17, 1948 2,447,564 Carnahan Aug. 24, 1948 2,497,103Toth Feb. 10, 1950 2,501,620 Skellett Mar. 21, 1950 2,546,987 EannarinoApr. 3, 1951 2,588,031 OBrien Mar. 4, 1952 2,808,507 Pawlowski Oct. 1,1957

